A variety of pelvic floor disorders such as urinary control disorders, fecal control disorders, interstitial cystitis, sexual dysfunction and pelvic pain are influenced by the sacral nerves. In particular, the organs involved in various bodily functions receive much of their control via the second, third, and fourth sacral nerves, commonly referred to as S2, S3, and S4, respectively. The sacrum, in general, is a large, triangular bone situated at the lower part of the vertebral column, and at the upper and back part of the pelvic cavity. The spinal canal runs throughout the sacrum. The sacral nerves pass through the sacrum via the anterior and posterior sacral foramina. These organs are also innervated via other nerves, such as the pudendal nerve.
Electrical stimulation of the sacral nerves, pudendal nerves, and other nerves of the pelvic floor has been found to offer relief for many pelvic floor disorders. For example, medical leads having discrete electrodes are implanted on and near the sacral nerves. An implantable pulse generator drives the electrodes with an electrical signal to stimulate the sacral nerves, and thereby restore or control bodily functions affected by pelvic floor disorders. Several techniques of electrical stimulation may be used, including stimulation of nerve bundles within the sacrum.
Chronic implantation of a pulse generator and lead for sacral nerve stimulation is typically preceded by a trial period. The trial period ordinarily has a prescribed maximum duration, but sometimes is exceeded by the patient or the physician. During the trial period, a clinician evaluates the efficacy of sacral nerve stimulation in alleviating the patient's disorder to determine whether the patient is a good candidate for chronic implantation.
The trial period ordinarily involves implantation of a temporary or chronic lead, and percutaneous connection of the lead to an external trial stimulator. Often, connection of the lead to the trial stimulator involves extensive subcutaneous tunneling of the lead to a percutaneous exit site. In addition, the percutaneous connection presents a significant risk of infection. To reduce infection risk, the lead is ordinarily tunneled away from the site selected for chronic implant, requiring added time and effort by the surgeon.
Neurostimulation efficacy and patient response can also be determined using a fully implantable neurostimulator specifically designed to operate during a brief trial period. Implantation of a neurostimulator with a limited power source or timed termination feature is disclosed in U.S. Publication 20040215287, to Swoyer et al., the entire content of which is incorporated herein by reference. The implantable trial neurostimulator described in the Swoyer et al. application is removed after the trial period and replaced with a chronic neurostimulator if the patient responds positively to the trial therapy.